The present invention relates to a high-pressure discharge lamp lighting apparatus system and, more particularly, to a high-pressure discharge lamp lighting apparatus system including a lighting apparatus for lighting a high-pressure discharge lamp such as a headlight of a vehicle, a high-pressure discharge lamp lighting apparatus, a lighting unit comprising the high-pressure discharge lamp lighting apparatus, and a vehicle in which the lighting unit is loaded.
In a conventional lighting apparatus used as a headlight of a vehicle to light a high-pressure discharge lamp, for example, luminous flux emitted from the high-pressure discharge lamp is made to rise quickly by supplying overcurrent to the high-pressure discharge lamp in a period immediately after the start of lighting until the lamp voltage rises adequately.
In addition, the conventional high-pressure discharge lamp lighting apparatus is constituted to supply a constant power to the high-pressure discharge lamp, in order to reduce the variation of the luminous flux emitted from the high-pressure discharge lamp in accordance with the irregularity in the characteristics or the characteristic variation based on the lifetime and the like in the high-pressure discharge lamp, in a stable state.
Incidentally, in the high-pressure discharge lamp of this kind, when turning on and turning off are repeated, its temperature variation causes the vapor pressure of a luminescent metal sealed therein to be varied and thereby the characteristics are varied.
For this reason, in the high-pressure discharge lamp for a headlight of a vehicle as described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-41075 (prior art), the power to be supplied to the lamp is controlled in accordance with a state of a cold lamp (a cold state) or a state of a hot lamp (a hot state).
As shown in FIG. 6, a high-pressure discharge lamp lighting apparatus 40 of the prior art comprises a lighting control circuit 41, a charging/discharging circuit 42 that is a series circuit constituted by a resistor R and a capacitor C, a stable lighting discrimination circuit 43, a power supply resetting circuit 44 and a level resetting circuit 45.
The charging/discharging circuit 42 constitutes a time measurement circuit for measuring the ON/OFF time of the power supply.
The lighting control circuit 41 adjusts the power to be supplied to a lamp (not shown) by a lighting circuit (not shown) on the basis of a value of terminal voltage Vc of the capacitor C.
The stable lighting discrimination circuit 43 discriminates whether the lamp is in the hot state or not. When the terminal voltage Vc is higher than the discrimination reference value, i.e. when the lamp is in the hot state, the stable lighting discrimination circuit 43 outputs stable lighting discrimination signal Ss that is to be at high level to the level resetting circuit 45.
The power supply resetting circuit 44 operates the lighting control circuit 41 if a predetermined resetting period has passed, when the power supply is turned on.
The level resetting circuit 45 charges the capacitor C during the resetting period when the stable lighting discrimination signal Ss is at high level.
That is, when the power supply is turned on (or when the lamp is lit up again), if the lamp is in the hot state, the capacitor C is charged and the lighting control circuit 41 restricts the power to be supplied to the lamp on the basis of the terminal voltage Vc of the capacitor C, during a predetermined resetting period.
The high-pressure discharge lamp lighting apparatus 40 of the above-described prior art can restrict the supply of the power in quantities more than necessary ones to the lamp when turning on and off the power supply (or turning on and off the lamp) is repeated in a short time, after the high-pressure discharge lamp has been in the stable state.
However, the discrimination reference value is used to discriminate whether the lamp is in the hot state or not, and the power to be supplied to the lamp at the voltage near the terminal voltage Vc is varied in stages.
If the terminal voltage Vc of the capacitor C is higher than the discrimination reference value, the capacitor C is charged during a predetermined resetting period even when the value of the terminal voltage Vc is a value near the discrimination reference value or a value at which the capacitor C is fully charged, and therefore the power to be supplied to the lamp is substantially the same, which means the power in the stable state.
On the other hand, if the terminal voltage Vc of the capacitor C is lower than the discrimination reference value, the overvoltage is supplied to the lamp even when the value of the terminal voltage Vc is near the discrimination reference value at which the lamp is in the hot state.
As described above, the high-pressure discharge lamp lighting apparatus 40 has the drawback that the power supplied to the lamp is varied in stages with reference to the discrimination reference value and thereby an optimal power responding to the lamp temperature cannot be supplied.